Recovery of aromatics by extraction or extractive distillation with solvent mixtures



Jan. 3Q, 196R8E KARL-HEINZ EISENLOHR ETA 3,366,568 l COVERY OF AROMA S BY EXTR ION EX ACTIVE DISTILLAT WITH SOLVE MI RES Filed Sept. 28, 1965 5 Sheets-Sheet 1 Mw/VVVN INVEKTORS v v A Avvvvgmg m/ y l( l XFMM ATTORNEYS Jan. 30, 19.68 KAR| -HE|N2 EISENLO'HR ETA 3,366,568

- Filed Sept. 28, 1965 RECOVERY OF' AROMATICS BY EXTRACTION OR E ACTIVE DISTILLATION WITH SOLVENT MIXTU RES 5 Sheets-Sheet 2 GVZVE @www INVENTORS Jan- 30, 1968 ARL-HEINZ Elsx-:NLOHR ETA 3,366,568

v RECOVE OF AROMATICS BY EXTRACTION OR E ACTVE DISTILLATION WITH SOLVENT MIXTURES Filed sept. 2a, 1965 I 5 sheets-sheet s,

.INVENTORS Jan- 30, 1968 KARL-HEINZ EISENLOHR ETAL 3,366,568

'RECOVERY OF AROMATICS BY EXTRACTION OR EXTRACTVE DISTILLATION WITH SOLVENT MIXTURES Filed Sept. 28, 1965 5 Sheets-Sheet 4 \\z/va%/vM/ .o

o 05 "o /Tamy I/ASCOS/W INVENTORS BY /w;

ATTORNEYS Jan. 30, 1968 KARL-HEINZ EISENLOHR ETAL 3,366,568

RECOVERY OF AROMATICS BY EXTRACTION OR EXTRACTVE DISTILLATION WITH SOLVENT MIXTURES Filed sept. 2e, 1965 l 5 Sheets-sheet 'o /VO/V HOMWCS HRW/7&5

@VS7/M7756 A 6 @gli ATTO NE INVENTORS United States Patent Oce 3,365,568 Patented Jan. 30, 1968 3,366,568 RECVERY F AROMATICS BY EXTRACTION 0R EXIRAC'ICIVE DSTHLLATION WITH SQLVENT MIXTURES Karl-Heinz lEisenlohr, Buehschlag, and Eckart Mller,

Eergenullnkheim, Germany, assignors to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany Filed Sept. 2S, 1965, Ser. Nn. 496,818 Claims priority, application Germany, Sept. 29, 1964, M 62,510 3 Claims. (Ci. 20S-313) The present invention provides an improved process for the recovery of aromatic hydrocarbons, especially benzene, toluene and xylene, from hydrocarbon mixtures containing the same, by extraction with water free solvent mixtures selective for aromatics which as a whole boil over the boiling point rangeof the aromatics to be recovered. The extraction with the solvent mixtures concerned is either a liquid-liquid extraction or an extractive distillation.

The recovery of aromatic hydrocarbons from hydrocarbon mixtures by liquid-liquid extraction or by extractive distillation with selective solvents has been practiced on a commercial scale for several decades. However, from the fact that again and again new solvents are suggested and patented for this purpose, it can be concluded that the ideal solvent has as yet not been found.

In addition to pure solvents, in many instances organic solvent mixtures have been proposed as the selective solvents. Furthermore, widely spread practice is to add certain quantities of water to the solvent. The addition of water offers the following advantages:

(l) The selectivity of the solvent is increased.

(2) The separation, especially of the higher aromatics, from the extract obtained is easily accomplished even with a small difference between the boiling point of the solvent and the aromatics because the aromatics distill azeotropically with water at temperatures under 100 C.

(3) The sump temperature in the distillation column employed for separation of the aromatics from the solvent extract is lowered so that not only are losses engendered by thermal decompositions reduced but also the heat energy required for heating the solvent to the sump temperature is lowered.

(4) With regard to liquid-liquid extractions a further advantage is that the lield of the existence of two phases is increased, so that larger quantities of aromatics may be contained in the feed stock Without leaving the twophase eld. Y

On the other hand, the following disadvantages of the addition of water must be taken into consideration:

(l) The solvent capacity for aromatics is reduced.

(2) The water is vaporized azeotropically with the aromatics to be separated from the solvent which causes substantial increase in the heat energy required. n

(3) In many instances the water causes undesired chemical reactions, especially hydrolysis.

A number of non-aqueous solvent mixtures have also become known, such as, for example, mixtures of SO2, ethylene glycol and formamide or mixtures which consist of a primary solvent which contains glycol derivatives and a secondary solvent such as methanol, ethanol and y Further proposals for solvents include, for example, (l) the combination of various glycol derivatives, (2) mixtures of two solvents of which the iirst contains l or 2 hydroxyl groups and the second contains 2 or more hydroxyl groups, (3) ethylene carbonate with additions of glycerol, ethylene glycol, pentaerythritol, formamide, forrnic acid, ethanol amines, monochlorohydrin, acetamide, resorcinol or hydroquinone as diluent, (4) alkane dinitriles, dimethyl hydantoin, N-alkylpyrrolidones, butyrolactone, cyan ethers of diethylene glycol, trior tetraethylene glycols or any desired mixtures of these solvents which are selective for aromatics or oletins.

However, without exception, no advantages over the use of a single solvent have been proved for these and many other proposals for the use of mixtures of various selective solvents boiling above the aromatics to be recovered for the liquid-liquid extraction or extractive distillation of aromatics, nor have any indications been given as to what quantity and in what proportions the various components of the mixture should be used in order to attain advantages over the use of single solvents.

The state of the art concerning the possibilities of use of solvent combinations for the liquid-liquid extraction or extractive distillation of aromatics can be summarized in that the effect of the addition of water to a solvent is known qualitatively, and that something is known concerning the properties of various combinations of glycol derivatives. However, from which points of view, solvents may otherwise be combined in order that they give good properties for liquid-liquid extraction or extractive distillation of aromatics has neither been described in scientific literature nor in the patent literature.

According to the invention, it was unexpectedly found that despite the large number of solvents known for these purposes and despite their very different types of chemical structure, certain rules exist, the application of which renders it possible to select from the boundless large nurnber of possible combinations, those which can be expected to have optimal properties.

Above all the following physical properties are desired in a selective solvent for the recovery of aromatics by liquid-liquid extraction or extractive distillation:

(l) High selectivity.

(2) High capacity.

(3) High aromatics range, that is, the formation of a two-phase system even at high aromatic concentrations.

.(ln the following, the highest aromatics concentration in the 3 substance system 'benzene-n-heptane-solvent at which a two-phase system is still present and above which separation into two phases no longer occurs is indicated as the aromatics range.)

(4) Low solubility of the solvent in the hydrocarbon phase.

(5) Low viscosity.

(6) High density.

(7) Boiling point above the boiling point range of the aromatics to be recovered.

(8) Thermal and chemical stability at boiling point.

(9) Melting point below ambient temperature.

It was ascertained that these various physical properties do not occur with complete irregularity in the individual solvents but rather that certain conformities to rules can be observed which are of special significance for the selection of a favorable solvent combination.

Of the properties given above, the third, namely, the aromatics range is especially suited as the classifying principle for dividing the solvents into certain groups. If the solvents are arranged according to increasing aromatics range they can be divided into three groups:

A. Solvents with low aromatics range. B. Solvents with high aromatics range and C. Solvents which do not have unlimited miscibility with aromatics.

A low aromatics range is one of less than 50% and preferably less than 35% is the maximum of the twophase region.

In the accompanying drawings:

FIGS. 1-6 show phase diagrams for 3 component systems of benzene, n-heptane and the selective solvent concerned;

FIG. 7 is a diagram showing the maximum quantity of benzene in the heavy phase (solvent phase) with respect to the composition of the solvent mixture N-methyl pyrrolidone (hereinafter referred to as NMP) and ethylene glycol;

FIG. 8 is a diagram showing the dependency of the selectivity of the composition of solvent mixture NMI and ethylene glycol;

FIG. 9 is a diagram in which the selectivity is plotted against the partition-coefficient in dependence on the composition of solvent mixture NMP `and ethylene glycol;

FIG. l is a phase diagram for the 3 component system NMF-ethylene glycol-benzene;

FIG. ll is a diagram showing the dependency of the viscosity of solvent mixture -NMP and ethylene glycol on its composition;

FIG. l2 schematically shows an apparatus for carrying out a liquid-liquid extraction according to the invention; and

FIG. 13 schematically shows an apparatus for carrying out an extractive distillation according to the invention.

A. Two typical phase diagrams are shown in FIGS. l and 2 for two typical solvents of the rst group (low aromatics range), namely, for N-methyl pyrrolidone and furfural, with indication of the partition equilibriums in the system solvent-benzene-n-heptane. The solvents of this group are characterized by their high capacity, low selectivity and high solubility of the solvent in the hydrocarbon phase. In view of their low selectivity the solvents of this group normally are only employed in combination with water whereby the above mentioned disadvantages must be accepted.

-It has now been found that most of the solvents of this group possess two other important and advantageous properties, namely, low viscosity and good thermal stability at the boiling point. Compounds with heterocyclic ring systems, such as, morpholine, N-methyl pyrrolidone, furfural, keto dioxane, and also dimethyl formarnide, aniline, ethylene diamine, nitrornethane, ethylene glycol mono-methyl ether, diethylene glycol mono-methyl ether, and others, all of which have an aromatics range below 35%, and diethylene triamine, triethylene tetrarnine, tetraethylene pentamine, butyrolactone, and dimethyl sulfoxide with aromatics ranges between 35 and 50% especially are illustrative of the group of solvents with low aromatics range.

IB. Solvents with a high .aromatics range, that is, solvents with an aromatic range of at least 50% in the maximum of the two phase system belong to the second group. They are therefore near the solubility limit with aromatics, for example so that they are miscible in .all proportions with benzene but not with xylene. Phase diagrams as in FIGS. l and 2 are given in FIGS. 3 and 4 for sulfolane and ethylene carbonate which are representatives of this group.

There are solvents of this group which have very high selectivity with good capacity, the latter, nevertheless, being lower than that of the solvents of Uroup A. As a consequence, solvents of group B would be the ideal solvents for the extraction of aromatics insofar as only the selectivity and capacity is taken into consideration, but remarkably they without exception possess other physical properties of such unfavorable values that they must be considered substantial disadvantages. Above all, representatives of this group all have the disadvantages that they are no longer stable at their boiling point and have a high viscosity. In addition, their melting points in some instances are above normal temperat-ure.

Compounds with double bonded oxygen and dinitriles, such as, for example, sulfolane, ethylene and propylene carbonate, oxy, thioand imino-dipropionitrile, monomethyl formamide and tetraethylene glycol especially are illustrative of group B solvents.

C. The solvents of the third group have a miscibility gap with aromatics. Phase diagrams of representatives of this group, namely, diethylene glycol `and propylene glycol, are given in FIGS. 5 and 6. Representatives of this group which dissolve less than 25% of benzene at 20 C. are preferably employed. Their capacity is less than that of the solvents of both other groups. Their selectivity is better than that of solvents of the iirst group and mostly less than that of solvents of the second group. Almost all have a high viscosity. Thermal stability at the boiling point is sometimes given. This group mostly contains chain compounds with one or more hydroxyl groups often also compounds with amino groups, such as, for example, ethylene glycol, diethylene glycol, propylene glycol, mono, diand triethanol amine, 1.4-cyclol1exane dimethanol, diglycol amine, formamide, malondinitrile, hydrazine and others.

According to the invention it was found that solvent mixtures could be obtained which have substantially better properties than could be expected from the rule of mixtures by mixing a solvent belonging to the first group (A) `with a solvent belonging to the third group (C). In each instance the selectivity is better than could be expected from the rule of mixtures and in some instances ever higher than of each of the individual components of the mixture. The ability to take up aromatics with solvents of group A is limited by their low aromatics range, and with solvents of group C by their low solvent capacity for aromatics. The combination of a solvent of group A with a solvent of group C results in a mixture having an ability to take up aromatics which is always better than that of each component and which often exceeds that of the component with the best take up ability by 50% and more.

An undesirable characteristic of solvents of groups C is their high viscosity. In this respect also, an unexpected advantage also is found in the combinations according to the invention as the viscosity of the solvent mixture is always less than could be expected from the rule of mixtures.

In addition, it was found that the best mixing solution for the various solvent mixtures can quickly be found according to a very definite method:

One investigates the three component system, solvent A-solvent C-benzene, determines the solubility limits and then the critical point (plait point) that is, the point where at the solubility limit the volumes of the light and heavier phases are equal. The composition at this point is the most favorable composition for the liquid-liquid extraction or extractive distillation of aromatics.

The critical point for a particular composition of a solvent A and solvent C, with the prerequisite that solvent A and benzene and solvent A and solvent C are completely miscible and that solvent C and benzene have a miscibility gap, is determined as follows:

Equal parts by volume of benzene and Solvent C are placed in a vessel. Two phases are formed, one of which predominantly contains benzene-generally the lighter phase-in the following designated as the IIC-phase (hydrocarbon phase) and one which predominantly contains solvent C--generally the heavy phase-designated in the following as the S-phase (solvent phase). Then small increments of solvent A are added while observing how both phases behave or change with respect to each other. When a certain quantity of solvent A has been added the phase separation line will suddenly disappear and only one phase will be present. lf by chance the volumes of the phases have been equal just before disappearance of the phase separation line the critical point would already have been determined. The critical point lies between the composition where two phases are last observed and the composition at which the phase separation line disappears. Usually, however, the volumes of the phases will be different and shortly before disappearance of the phase separation line the phase present in the larger quantity will be a multiple of the other phase. The procedure which follows under such circumstances depends upon which of the two phases was the larger just before disappearance of the phase separation line. If the HC- phase is the smaller one, small increments of benzene are added to the mixture until the mixture becomes cloudy and again separates into two phases. If at this point the HC-phase is still the smaller one, then a mixture of equal parts of benzene and solvent A are added in small increments until the phase separation line again disappears so that only one phase is present. Thereafter this procedure is repeated, that is, so much benzene is added until clouding and phase separation occurs and then so much of an equal mixture of benzene and solvent A is added until the phase separation line disappears, at some point the condition will occur in which the S-phase rather than the HC-phase is the smaller. At this point the critical point has already been exceeded and one can usually determine its position by interpolating between the last and second last measuring point. However, if this is not believed sufficiently accurate, because the quantities added were selected too large, several mixtures are prepared which are near the critical point and which still just separate into two phases and a mixture of equal quantities of benzene and solvent A is added thereto in small increments. The mixture in which the two phases are of equal volume just lbefore the phase separation line disappears corresponds to the composition of the critical point.

If, on the other hand, the S-phase is smaller just before disappearance of the phase separation line during the first addition of solvent A the procedure is analogous but the benzene added to cause phase separation is replaced by solvent C and the mixture of equal parts of benzene and solvent A added to cause disappearance of the phase separation line is replaced by a mixture of equal parts of solvent C and solvent A and the procedure repeated until the S-phase just becomes the larger phase and the critical point interpolated or determined analogously to the above procedures.

When the feed stock from which the aromatics are to be recovered is one in which the non-aromatics predominantly are paraflins or if a paraflinic antisolvent is used the quantity of solvent C in the mixture can Ibe 5 to less than previously defined. If, on the other hand, the non-aromatics in the feed stock contains large quantities of olefins and/ or naphthenes it often is expedient to increase the quantity of solvent C in the mixture about 5 to 10%.

These relationships are more fully explained in the following with reference to FIGS. 7-11 withthe mixture of N-methyl pyrrolidone (subsequently abbreviated as NMP) and ethylene glycol as example. As can be seen from FIG. 7 the ability to take up aromatics of a mixture of a solvent of group A (NMP) and a solvent of group C (ethylene glycol) is better than that which corresponds to the rule of mixtures and is represented by the broken line A-C. In general, the ability of a solvent mixture of a solvent of group A with a solvent of group C to take up aromatics is greater than that of each solvent individually. In the illustration given the maximum take up is achieved with a mixture of 55% of ethylene glycol and 45% of NMP and amounts to 55 weight percent of benzene in the heavy phase.

The dependency of the selectivity upon the solvent mixture composition, once for 10% benzene and once for 40% benzene in the light phase, is shown in FIG. 8. Both curves run through a maximum which lies at 70480% of ethylene glycol. The maximum abilityto take up aromatics therefore is at a diiferent composition than for the selectivity maximum. Which solvent composition is optimal economically is a real compromise between optimal selectivity and optimal take up ability.

The manner in which the optimum between selectivity and capacity can be determined is shown in FIG. 9. In such figure the capacities (partition coecients) and the selectivities for different mixing ratios of NMP and ethylene glycol are respectively plotted as abscissa and ordinates. vIn order that the entire system could be included an aromatics content of 10% in the light phase was made the basis. It can be seen that the points of the individual mixtures lie far above and to the right from the line A-C and therefore towards values of higher capacity and higher selectivity. It furthermore can be seen that the range which extends furthest up and right and therefore the optimal economic range lies between 50 and 60% ethylene glycol.

This value of about 55 glycol is also found when the three component diagram of both solvents with benzene is investigated and the critical point is determined as described above. FIG. 10 gives the diagram for the system NMP-ethylene glycol-benzene. At the critical point P the ratio ofethylene glycol to NMP is 55 :45.

Further examples of optimal mixtures of solvents of group A with solvents of group C are as follows:

Solvent mixture components: Weight, percent N-methylpyrrolidone 35.55 Diethanolamine 64.45 Aniline 52.1 Monoethanolamine 47.9 Butyrolactone 36.56 1.4-cyclohexanedimethanol 63.44 Phenol 38.5 Ethylene glycol 61.5 Aniline 57.0 Ethylene glycol 43.0 Phenol 50.7

lGlycerine 49.3 N-methylpyrrolidone 28.4 1.4-cyclohexanedimethanol 71.6 Dimethylformamide 26.78 1.4-cyclohexanedimethano1 73.22 Aniline 44.29 1.4-cyclohexanedimethanol 55.71 Phenol 34.5 1 .4-cyclohexanedimethanol 65 .5 Furfural 46.40 1.4-cyclohexanedimethanol 53.60 Butyrolactone 64.92 Formamide 35.08 Dimethylsulfoxide 77.78 Formamide 22.22 Butyrolactone 28.24 Malonnitrile 71 .76

N-methylpyrrolidone 21.2 Malonnitrile 7 8.8 Dimethylsulfoxide 47.2 Monoethanolamine 52.8 Dimethylformamide 23.4 Malonnitrile 76.6 Dimethylsulfoxide 35.1 Malonnitrile 64.9 Dimethylformamide 60.8 Formamide 39.2 N-methylpyrrolidone 58.99 Glycerine 41.01 Dimethylsulfoxide 62.3 Ethylene glycol 37.7 Dimethylformamide 74.24 Glycerine 25.76 N-methylpyrrolidone 64.24 Formamide 35.76

7 Solvent mixture components: Weight, percent Dimethylformamide 39.2 Ethylene glycol 60.8 Dimethylformarnide 33.4 Monoethanolamine 66.6 N-methylpyrrolidone 10.2 Diethylene glycol 89.8 N-methylpyrrolidone 33.2 Monoethanolamine 66.8 Butyrolactone 52.0 Ethylene glycol 48.0 Diethylene triamine 80.1 Ethylene glycol 19.9 N-methylpyrrolidone 45 .0 Ethylene glycol 55.0 Aniline 56.5 Formamide 43.5 Furfural 70.2 Monoethanolamine 29.8 Furfural 69.5 Formamide 30.5 Phenol 50.7 Monoethanolamine 49.3 Phenol 54.1 Formamide 45.9

It also can be seen from FIG. 11 that the viscosity of a mixture of NMP and ethylene glycol, above all in the middle range, is signicantly lower than was to be expected from the rule of mixtures.

The present invention is generally suited for the recovery of aromatics from hydrocarbon mixtures containing aromatica by liquidliquid extraction or extractive distillation and also for the recovery of extracts in which the concentration of aromatics in the hydrocarbon extracts has only been increased over that in the starting mixture. An especial advantage of the process according to the invention is that it also is adapted for the recovery of high purity aromatica, which in recent times have assumed considerable significance as starting materials for chemical syntheses.

The process according to the invention renders it possible to recover aromatics whose non-aromatics content is below 0.1% and even under 0.01% without diiculty. Even higher purity requirements such as absence of nonaromatics in quantities capable of chromatographic detection can be achieved according to the invention.

The invention is further illustrated by the following examples and FIG. 12 and FIG. 13 which diagrammatically show the apparatus employed in such examples.

Example 1 1389 kg./h. of a feed stock of the following composition Weight, percent B=benzene 29.7 T=toluene 31.3 X=xylene 11.0 P=parainic hydrocarbon 18.4

N--enaphthenes Weight, percent B 7.0 T 5.2 X 1.8 P 0.5 N 4.9 Solvent 80.6

were withdrawn from the bottom of extractor 2 and supplied to the preliminary distillation column 4 over con- 8 duit 3. Column 4 had 40 actual trays and was operated with a reflux ratio of 2:1. 725 kg./h. of the head product which in round numbers consisted of about l/s of aromatics and the remainder mainly naphthenic non-aromatics, namely,

Weight, percent B 28.5 T 3.5 P 6.0 N 60.0 Solvent 2.0

was recycled to extractor 2 as retlux over line 5. This head product contained all of the non-aromatics originally contained in the extract. 389 kg./h. of an aromaticsfree rainate of the composition P2654 weight percent and N=34.6 weight percent, were withdrawn from the extractor through line 6.

8085 kg./h. of a non-aromatics -free extract of the composition Weight, percent B 5.1

X 1.9 Solvent 87.6

were Withdrawn from the sump of column 4 through line 7 and supplied to solvent stripper 8 which contained 2O actual trays and was operated with a reliux ratio of 0.5: l. 1000 kg./h. of pure aromatics of the composition Weight, percent B 41.2

were taken olf overhead through conduit 9. The sump product (7085 kg./h.), which was practically pure solvent mixture, was recycled to extractor 2 through line 10. The aromatics mixture taken otf overhead from stripper 8 was distilled in a known manner to separate it into its components. The benzene recovered had a melting point of 5.50 C., the toluene recovered had a refractive index nD2=1.4967 and no non-aromatics were discernable gas chromatographically in the xylene fraction.

Example 2 .1000 kg./h. of the benzene cut of a hydrogenated pyrolysis gasoline of the following composition:

Weight, percent Benzene=B Non-aromatics boiling under 75 C=NA 75 9 Non-aromatics boiling between 75-105 C--NA 105 9 Methyl cyclohexanezMCH 2 B 25 NA 75 36 NA 36 MCH 8 So much heat was supplied to the sump of the column that, with the withdrawal of 250 kg./h. of distillate from the head of the column, a reflux ratio of 8:1 was maintained at the head ofthe column.

A mixture of 4500 kg./h. of solvent mixture and 750 kg./h. benzene was Withdrawn from the sump of column 12 and supplied through conduit 15 to the 20th tray of the 40 tray column 16. 750 kg./h. of substantially pure benzene were withdrawn fromthe head of column 6 through 9 conduit 17. Such benzene had a melting point of 5.50" C. and as a maximum contained 0.02% of MCH as impurity.

So much heat was supplied to the sump of column 16 in the yform of steam that, with the withdrawal of the 750 kg./h. of benzene from the head thereof, a reflux ratio of 0.5:1 was maintained at the head of the column.

The benzene free NMP ethylene glycol mixture (4500 kg./h.) which accumulated in the sump of column 16 were recycled to column 12 over conduit 13.

We claim:

1. A process for separating a hydrocarbon mixture containing aromatic and non-aromatic hydrocarbons into fractions of different degrees of aromaticity by treatment with a solvent mixture and recovering a more concentrated aromatics fraction from said mixture which comprises contacting the mixture with a water free solvent mixture which as a Whole boils above the aromatics to be recovered, said solvent mixture consisting of solvent (A), N-methyl-pyrrolidone, and solvent (C), ethylene glycol, the ratio of the quantity of said solvent Ato the quantity of said solvent C in said solvent mixture being from X:Y to X:YilO Weight percent, the ratio X:Y being the ratio of solvents A and C at the critical point in the three component system solvent A, solvent C and benzene, said solvent mixture being a mixture of 45 to 65 weight percent of ethylene glycol and 55 to 35 weight .percent of N-methyl-pyrrolidone, eecting phase separation of the phases thus formed, an extract phase in which the hydrocarbons extracted from said mixture has a higher aromatic concentration than said mixture and a raffinate phase less aromatic than said mixture and distilling an aromatics rich hydrocarbon traction from the solvent mixture in said extract phase.

2. The process of claim 1 in which said hydrocarbon mixture and said solvent mixture are contacted with each other in a liquid-liquid extraction process.

3. The process of claim 1 in which said hydrocarbon mixture and said solvent mixture are contacted with each other in an extractive distillation process.

References Cited OTHER REFERENCES Perry: Chemical Engineers Handbook, Third Edition, 1950, pages 719 to 730.

Weissberger: Technique of Organic Chemistry, volume IV, Distillation, 1951, page 338, Interscience Publishers Inc., N Y.

HERBERT LEVINE, Primary Examiner.

DELBERT E. GANTZ, Examiner. 

1. A PROCESS FOR SEPARATING A HYDROCARBON MIXTURE CONTAINING AROMATIC AND NON-AROMATIC HYDROCARBONS INTO FRACTIONS OF DIFFERENT DEGREES OF AROMATICALLY BY TREATMENT WITH A SOLVENT MIXTURE AND RECOVERING A MORE CONCENTRATED AROMATICS FRACTION FROM SAID MIXTURE WHICH COMPRISES CONTACTING THE MIXTURE WITH A WATER FREE SOLVENT MIXTURE WHICH AS A WHOLE BASIS ABOVE THE AROMATICS TO BE RECOVERED, SAID SOLVENT MIXTURE CONSISTING OF SOLVENT (A), N-METHYL-PYRRLIDONE, AND SOLVENT (C), ETHYLENE GYLCOL, THE RATIO OF THE QUANTITY OF SAID SOLVENT A TO THE QUANTITY OF SAID SOLVENT C IN SAID SOLVENT MIXTURE BEING FROM X:Y TO X:Y$10 WEIGHT PERCENT, THE RATIO X:Y BEING THE RATIO OF SOLVENTS A AND C AT THE CRITICAL POINT IN THE THREE COINPONENT SYSTEM SOLVENT A, SOLVENT C AND BENZENE, SAID SOLVENT MIXTURE BEING A MIXTURE OF 45 TO 65 WEIGHT PERCENT OF ETHYLENE GLYCOL AND 55 TO 35 WEIGHT PERCENT OF N-METHYL-PYRROLIDONE, EFFECTING PHASE SEPARATION OF THE PHASESE THUS FORMED AN EXTRACT PHASE IN WHICH THE HYDROCARBONS EXTRACTED FROM SAID MIXTURE HAS A HIGHER AROMATIC CONCENTRATION THAN SAID MIXTURE AND A RAFFINATE PHASE LESS AROMATIC THAN SAID MIXTURE AND DISTILLING AN AROMATICS RICH HYDROCARBONS FRACTION FROM THE SOLVENT MIXTURE IN SAID EXTRACT PHASE.
 3. THE PROCESS OF CLAIM 1 IN WHICH SAID HYDROCARBON MIXTURE AND SAID SOLVENT MIXTURE ARE CONTACTED WITH EACH OTHER IN AN EXTRACTIVE DISTILLATION PROCESS. 